Abstract: To date, the diffusion method which measures the isotope values of ammonium and nitrate of soil extraction is extensively applied. But we still lack a systematic method to evaluate the isotope discrimination effect in ¹⁵N labeled experiments, mainly due to the high ¹⁵N abundance and its variation during the incubation period. Here, we presented some efficient improvements of the diffusion method including using 10 μL KHSO₄ as the ammonia absorption liquid, setting the gas to liquid ratio to 4:1, lowering the use of MgO and Devarda alloy to 250 mg, and selecting 25 ℃ as the incubation temperature. We used this improved method to measure the inorganic nitrogen isotope abundance of solutions with both high and low nitrogen contents. The results indicated that there was no significant difference between theoretical and measured values. Therefore, our improvements are useful to measure ammonium and nitrate isotope ratios of ^15N labeled experiments.

Key words: foraging behavior, red-crowned crane, stable isotope, food chain